1. Field of the Invention
The present invention relates to what is called a face bow of a mandibular motion diagnostic device, more particularly to a face bow as a component of a device for measuring a patient's mandibular motion and reproducing it precisely by the use of a mandibular model on the basis of the measured data, which is attached in a fixed positional relationship to the patient's mandible as measurement is taken of the motion thereof and is shifted onto the mandibular model upon completion of the measurement so that the patient's dental arch in its actual position is precisely reproduced in the mandibular model.
2. Prior Art
In view of the significance of the mandibular motion in dental analyses, various methods and devices for measuring the mandibular motion have been proposed. They are, however, invariably mere measuring devices, having nothing to do with reproduction of the mandibular motion.
The present inventor has, therefore, further developed the idea to supply the information obtained about the mandibular motion by such a measuring device to a reproducing device so as to have the patient's mandibular motion precisely reproduced thereby, and which could thus provide a far more realistic diagnostic device than its earlier counterparts which are good soley for measuring.
This diagnostic device is based on the idea of imaginarily setting an isosceles triangle with the center of the anterior section of the mandible as the vertex and the posterior ends of the lateral sections thereof as the base points, assuming the plane defined by this isosceles triangle as a rigid plane representing the mandible, and grasping the mandibular motion as three-dimensional motion of this plane. In particular, this invention consists of setting the points to be measured (measuring points) at points which correspond to the above-mentioned three points each consisting of a spot light sources, measuring the amount of displacement of the individual measuring points and converting the measured amount of displacement in the computing unit into corresponding two-dimensional coordinate data to be stored as position information in the memory unit.
Meanwhile, in the reproducing unit three reference points for reproduction are set where their positional relationships to the mandibular model are equal to those between the above-mentioned measuring points and the patient's mandible. These reference points for reproduction are connected with respective drive units and the position information read out of the memory unit is inputted to the individual drive units so that the plane representing the mandible defined by the three reference points for reproduction is caused to move with the reference points for reproduction as datum points for motion; and as a result, the mandibular model is caused to precisely reproduce the three-dimensional motion of the patient's mandible. Details thereof are disclosed in the specification of an earlier application filed in the name of the present applicant (Japanese patent application No. Sho-57-57721) which is incorporated herein by reference and hence description of any further details is omitted here. In this diagnostic device, however, one thing remains unsolved; that is, the problem of how to locate precisely the patient's dental arch in the mandibular model in the process of reproducing the structure of the patient's mandible. Even if the motion of the whole mandible except for the dental arch could be precisely reproduced, failure to reproduce the position of the critical dental arch in the mandibular model is bound to make such information imperfect for diagnostic purpose. Hitherto there was known a means of actually measuring the position of the dental arch in the patient's mandible and shifting it onto an articulator, the means having nothing to do with such a reproducing device. This means includes a reference bar called "face bow" linking the patient's auricular holes with the bottoms of his orbits and a dish-retaining bar having fixedly attached to it a dental dish filled with an impression material for taking the impression of the dental arch. These are connected together and the face bow is further connected as it is used with a separate head fastening member freely adjustable in length, freely rotatable and tiltable. The above-mentioned face bow is set on the patient's head and the dental dish in the patient's mouth cavity. The head fastening member is then fastened to the face bow and the dental dish steadied with respected to each other and the patient is ordered to bite the impression material. The bitten impression material is then taken out, the face bow is released from the head and is shifted onto the articulator. The articulator has provided thereon a reference plane corresponding to the auricular holes and the bottom of the orbits; and when the occlusal impression on the dental dish is set thereon together with the face bow fixedly connected with the dental dish, the positional relationship between the articulator and gnathic model can be grasped. Such a conventional means, although it is somehow applicable to the above-mentioned reproducing system, can hardly have either the auricular holes or the bottom of orbits as accurate reference points therefor and errors of approximately 1 mm are inevitable. Accordingly, the high precision of motion in the reproducing system is bound to be affected thereby.